The present invention relates to an electromagnetic clutch motor having an electromagnetic power transmission mechanism, adapted for use as the driving source of an industrial sewing machine.
In this type of electromagnetic clutch, a cluch disc and a brake disc slide along a spline formed on an output shaft to transmit the driving torque and braking torque. Electromagnetic clutches of the kind described are being used in increasing numbers as the driving power source of industrial sewing machines. In such uses, a large pulsation of the torque is caused to generate a loud noise due to the presence of play between the spline and the discs. The magnetic circuit has three gaps. Two out of these three gaps are radial gaps so that they do not produce any attracting force. These two gaps, however, are inevitably large because they are the gaps between a rotary part and a stationary part. In consequence, the magnetic circuit does not efficiently generate an attracting force in response to the electric input (ampere-turns) to the clutch coil and the brake coil.